Softening rubber



Patented Oct. 19, 1943 Rani-tap. Rgibiiiijii,

signorf to American 1 f Ntnawmg; a

This invention relates to the treatment of rubber and more particularly to a method of treating rubber to obtain a product of increased softness or plasticity.

It is known" to mill the crude rubber in the presence of oxygen, e. g., air. The milling causes a softening or breakdown of the rubber which facilitates the subsequent processing (calendering, tubing, etc.) of the rubber or compounded rubber.

It is an object of the present invention to provide a process for accelerating the rate ofbreakdown of unvulcanized rubber and for increasing its plasticity. It is a further object to provide an unvulcanized rubber of increased'plasticity. It is an additional object to provide a new class of rubber plasticizing agents. i

The foregoing objects may be accomplished in accordance with my invention by subjecting unvulcanized rubber to the action of a small amount of an S-alkyl (long chain) isothiourea hydrochloride, as by milling the rubber therewith for a short time. These compounds may be represented by the following generalformula: 1

R s-c=NH v I: I IHz in which R is an aliphatic hydrocarbon group containing a straight chain of at least about 10 carbon atoms, such as decyl, lauryl, myristyl,

palmityl, stearyl, oleyl, etc; The aliphatic chain may be branched or unbranched.

For maximum gain in plasticity, the plasticizing agent is added to the rubber as early as possible in the milling operation, such as just after the preliminary milling or knitting together of =the rubber, and preferably in the absence of com- \pounding ingredients, especially sulfur.

In general, the amount of plasticizing agent to be added will not be much above about 1% on -the weight of the rubber, for example about 0.375%. Larger amounts may be used if desired but without proportionate increase in plasticizing efiect. The plasticizing agents may be used singly, or more than one may be added to the rubber either separately or in admixture.

The plasticizing agents will be morev effective at elevated temperatures, e. g. above about 50 C; Any temperature to which rubber may be heated without detrimental effect may be used, for ex ample'up to about 160 0.

My invention is further illustrated by the fololdre eiivvichlConni, as

Cyanamid Company, 1

atioir pplication' March" ese ial 5 2 J 8 Claims. (ClJ 2'60-'7'61) decyl, 59% lauryl, 22%

4 stearyl) long chain isothiourea hydrochloride.

milled for an additional 5 s lowing specific example to which, however, the

in accordance with a modification of the wellknown Zimmerman and Cooper method, Ind. and Eng. Chem. 20, 812 (1928). The plasticity measurements were made in a Williams plastometer at 100 C. using a 3 minute Y value.

' Example A control of 420 grams of crude rubber (smoked sheets) was placed on a 12 inch mill, the rolls of which had an initial temperature of C. After milling for 5 minutes, 20 grams of rubber (A) were removed and the remainder milled for a' further 5 minutes (B).

A sample of 420 grams of smoked sheets was milledunder the same conditions for 5 minutes when 20 grams of the rubber were removed (A). To the remainder of the added 1.5 grams of a mixed (approximately 3.4% myristyl, 11% palmityl,

This rubber was then minutes (B).

The A and B rubber of both the control and the sample were cooled to room temperature be- Suitable variations and changes may be made in the invention without departing from the spirit thereof or the scope of the following claims.

I claim: 1. A process of increasing the plasticity of rubher which comprises, milling unvulcanized rub- 1 her with a small amount of a compound of the following general formula:

2. A process in accordance with claim l, in.

which R is lauryl.

3. A process in accordance with claim 1, in which R is palmityl.

4. A process in accordance with claim 1, in which R. is stearyl. I

rubber on the rolls was conditions in the absence 5. Unvulcanized rubber of increased plasticity obtained by melting amount of a compound formula:

RSG=NH 11101 in which a a a inflame hidmerbon weal selected from the group consisting of decyl, l'auryl, myristyl, palmityl, stearyl and oleyl, for

a time sufilcient to effect an increase in the plus the rubber with a small of the following general ticity or the rubber over that which would have ii subjected to the same conditions the absence of said compouhd. 6. Unvulcanized rubber of increased obtained by milling the amount of S-lauryl isothiourea hydrochloride, for a time sufllcient to eflect an increase in ph rubber with a obtained by milling the rubber '(o'r avtime'sumcient to efiect an increase in the rubber over that which the rubplflticity of the if subjected to the same condiher would have tions in the absence of said isothiourea hydroticity of the rubber over that which t e 1 chloride.

- RICHARD O. ROBLIN, JR. 

